Image coding apparatus and image decoding apparatus

ABSTRACT

An image coding apparatus inputs pixel data of a part image of high resolution. An upper layer coding portion ( 101 ), a second shape data generating portion ( 102 ), and a second shape data coding portion ( 103 ) perform coding of shape data and pixel data in the upper layer. A down sampling portion ( 104 ) generates pixel data of low resolution. A lower layer coding portion ( 105 ), a first shape data generating portion ( 106 ), and a first shape data coding portion ( 107 ) code shape data and pixel data in the lower layer.

TECHNICAL FIELD

[0001] The present invention relates to an image coding apparatus and animage decoding apparatus, and more particularly to a motion image codingapparatus for coding image data in an efficient manner and a motionimage decoding apparatus for decoding the coded data generated by themotion image coding apparatus, used in the field of digital imageprocessing.

BACKGROUND ART

[0002] In image coding, a method of superimposing different motion imagesequences has been considered. An article titled “An Image Coding SchemeUsing Layered Representation and Multiple Templates” (Technical Reportof IEICE, IE94-159, pp. 99-106 (1995)) describes a scheme forsuperimposing a motion image sequence as a background and another motionimage sequence of a component or part image (e.g., video image of ahuman figure or fish cut out by chromakey technique) as a foreground, togenerate a new image sequence.

[0003]FIG. 12 is a block diagram showing a coding apparatus and adecoding apparatus according to the conventional art. A pixel datacoding portion 1201 in FIG. 12 is a portion for coding pixel datarepresenting intensity and color difference, and a shape data codingportion 1202 is for coding shape data representing a shape of partimage. These portions constitute an apparatus for coding a part image.

[0004] Shape data are used for coding pixel data. A pixel data decodingportion 1203 in FIG. 12 is a portion for decoding pixel data, and ashape data decoding portion 1204 is for decoding shape data. Theseportions constitute an apparatus for decoding a part image. For decodingpixel data, decoded shape data are used.

[0005] Shape data coding portion 1202 first expresses a contour of ashape using 8 directional chain codes, for example, and then codes thechain codes by Huffman coding. Pixel data coding portion 1201 codespixel data by the international standard method of coding motion images,such as MPEG or H.261. When pixel data are divided into blocks, anarbitrary shape DCT technique or the like is employed for the blockincluding a boundary of part image.

[0006] Each part image is decoded by a decoding apparatus, and thensuperimposed at a superimposing portion (not shown) using shape data,and displayed on a device like a display. For example, whensuperimposing a part image p (i, j) in arbitrary shape on a rectangularbackground image b (i, j), a display image f (i, j) is generated usingshape data s (i, j) according to the following expression (1):

f(i, j)=p(i, j) s(i, j)+b(i, j)[1−s(i, j)]  (1)

[0007] wherein (i, j) represents a coordinate of a pixel, and f (i, j)represents a pixel value. s (i, j) assumes the value “1” within a partimage, and “0” outside the part image.

[0008] In the conventional art, however, there has not been proposed atechnique for setting up spatial hierarchy for a part image. Theinternational standard MPEG2 method realizes hierarchy (i.e., spatialhierarchy) over an entire image. In the method, data in a lower layerhaving low spatial resolution throughout the entire image and data in anupper layer for improving the resolution are decoded together to achievehigh spatial resolution.

[0009] Accordingly, an object of the present invention is to provide animage coding apparatus and an image decoding apparatus that can realizespatial hierarchy in a part image.

[0010] To obtain shape data of low resolution, high-resolution shapedata obtained by the conventional art may simply be thinned out.However, if thus obtained low-resolution image is displayed on alarge-screen monitor having low resolution, the contour of a part willhave stepwise appearance, which leads to deterioration in psychic imagequality. The same problem arises when a low-resolution image is enlargedfor display on a large-screen monitor having high resolution.

[0011] Accordingly, another object of the present invention is toprovide an image coding apparatus and an image decoding apparatus thatcan solve the above problem.

DISCLOSURE OF THE INVENTION

[0012] In the present invention, an image coding apparatus and an imagedecoding apparatus as described in the following (1) through (10) areprovided to solve the above-described problems.

[0013] (1) An image coding apparatus performing lower layer coding forcoding a part image in arbitrary shape in low resolution and upper layercoding for coding the part image in high resolution, comprising: a firstshape data generating portion for generating low-resolution shape datarepresenting the arbitrary shape; a first shape data coding portion forcoding the generated low-resolution shape data; a second shape datagenerating portion for generating high-resolution shape datarepresenting the arbitrary shape; and a second shape data coding portionfor coding the generated high-resolution shape data; wherein thelow-resolution shape data are used for coding the part image in thelower layer, and the high-resolution shape data and the decoded partimage data in the lower layer are used for coding the part image in theupper layer.

[0014] (2) The image coding apparatus according to (1), wherein thesecond shape data coding portion codes information on difference betweenthe high-resolution shape data and the low-resolution shape data.

[0015] (3) An image coding apparatus performing lower layer coding forcoding a part image in arbitrary shape in low resolution and upper layercoding for coding the part image in high resolution, wherein highresolution shape data of the part image are shared by the upper andlower layers; the apparatus comprising a high-resolution shape datagenerating portion for generating high-resolution shape data of the partimage, and a shape data coding portion for coding the generatedhigh-resolution shape data; wherein high resolution shape data having Nlevels of gradation (N is at least 2) are transformed to low-resolutionshape data having M levels of gradation (M>N), the low-resolution shapedata are used for coding the part image in the lower layer, and thehigh-resolution shape data and the decoded part image data in the lowerlayer are used for coding the part image in the upper layer.

[0016] (4) An image decoding apparatus for decoding data coded by theimage coding apparatus according to (1), performing lower layer decodingfor decoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution; theapparatus comprising: a first shape data decoding portion for decodinglow-resolution shape data, and a second shape data decoding portion fordecoding high-resolution shape data; the low-resolution shape data areused for decoding the part image in the lower layer, and thehigh-resolution shape data and the decoded part image data in the lowerlayer are used for decoding the part image in the upper layer.

[0017] (5) An image decoding apparatus for decoding data coded by theimage coding apparatus according to (2), performing lower layer decodingfor decoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution; theapparatus comprising: a first shape data decoding portion for decodinglow-resolution shape data, and a second shape data decoding portion fordecoding high-resolution shape data; wherein the low-resolution shapedata are used for decoding the part image in the lower layer, and thehigh-resolution shape data and the decoded part image data in the lowerlayer are used for decoding the part image in the upper layer; and thesecond shape data decoding portion uses information on differencebetween the high-resolution shape data and the low-resolution shape datato obtain high resolution shape data.

[0018] (6) An image decoding apparatus for decoding data coded by theimage coding apparatus according to (3), performing lower layer decodingfor decoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution; whereinhigh resolution shape data of the part image are shared by the lower andupper layers; the apparatus comprising a shape data decoding portion fordecoding high-resolution shape data; wherein high resolution shape datawith N levels of gradation (N is at least 2) are transformed tolow-resolution shape data with M levels of gradation (M>N), thetransformed shape data are used for decoding the part image in the lowerlayer, and the high-resolution shape data and the decoded part image inthe lower layer are used for decoding the part image in the upper layer.

[0019] (7) The image coding apparatus according to (1), wherein thesecond shape data generating portion has a mode for generatinghigh-resolution shape data corresponding to a portion of the part imagecoded in the lower layer.

[0020] (8) The image coding apparatus according to (2), wherein thesecond shape data generating portion has a mode for generatinghigh-resolution shape data corresponding to a portion of the part imagecoded in the lower layer, and when the mode is selected, the secondshape data coding portion codes the high-resolution shape dataindependent of the low-resolution shape data.

[0021] (9) An image decoding apparatus for decoding data coded by theimage coding apparatus according to (7), performing lower layer decodingfor decoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution; theapparatus comprising: a first shape data decoding portion for decodinglow-resolution shape data, and a second shape data decoding portion fordecoding high-resolution shape data; wherein the low-resolution shapedata are used for decoding the part image in the lower layer, and thehigh-resolution shape data and the decoded part image data in the lowerlayer are used for decoding the part image in the upper layer; and thesecond shape data decoding portion has a mode for decodinghigh-resolution shape data corresponding to a portion of the part imagecoded in the lower layer.

[0022] (10) An image decoding apparatus for decoding data coded by theimage coding apparatus according to (8), performing lower layer decodingfor decoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution; theapparatus comprising: a first shape data decoding portion for decodinglow-resolution shape data, and a second shape data decoding portion fordecoding high-resolution shape data; wherein the low-resolution shapedata are used for decoding the part image in the lower layer, and thehigh-resolution shape data and the decoded part image data in the lowerlayer are used for decoding the part image in the upper layer; thesecond shape data decoding portion uses information on differencebetween the high-resolution shape data and the low-resolution shape datato obtain high-resolution shape data; and the second shape data decodingportion has a mode for decoding high-resolution shape data correspondingto a portion of the part image coded in the lower layer, and, when themode is selected, decodes the high-resolution shape data independent ofthe low-resolution shape data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a block diagram showing a coding apparatus according toa first embodiment of the present invention.

[0024]FIG. 2 is a block diagram showing a decoding apparatus accordingto the first embodiment of the present invention.

[0025]FIG. 3 is a block diagram showing a coding apparatus according toa second embodiment of the present invention.

[0026]FIG. 4 is a block diagram showing a decoding apparatus accordingto the second embodiment of the present invention.

[0027]FIG. 5 is a block diagram showing a coding apparatus according toa third embodiment of the present invention.

[0028]FIG. 6 is a block diagram showing a decoding apparatus for a lowerlayer according to the third embodiment of the present invention.

[0029]FIG. 7 is a diagram for use in illustrating information ondifference between upper layer shape data and lower layer shape data.

[0030]FIGS. 8A through 8D are diagrams for use in illustrating atechnique for obtaining low-resolution shape data from high-resolutionshape data according to the present invention.

[0031]FIG. 9 is a block diagram showing a coding apparatus according toanother embodiment of the present invention.

[0032]FIG. 10 is a block diagram showing an example of an apparatus forperforming hierarchical coding of a part image according to the presentinvention.

[0033]FIG. 11 is a block diagram showing a lower layer decodingapparatus according to the present invention.

[0034]FIG. 12 is a block diagram showing a coding apparatus and adecoding apparatus in the conventional art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035] Hereinafter, embodiments of the present invention will bedescribed, though the present invention is not limited to thoseembodiments.

[0036] An apparatus shown in FIG. 10 is considered as means for settingup spatial hierarchy in a part image. A down sampling portion 1001 inFIG. 10 thins out pixels from input pixel data to lower spatialresolution of the pixel data. A second down sampling portion 1002 thinsout pixels from input shape data to lower spatial resolution of theshape data. The shape data show a shape of part image, and arerepresented as a binary image having a pixel value “1” within a part anda pixel value “0” outside the part, for example.

[0037] A lower layer coding portion 1004 codes pixel data of lowresolution. For the coding, the international standard method of codingmotion images, such as MPEG or H.261, is employed. When an image isdivided into blocks, an arbitrary shape DCT technique or the like isused for a block including a boundary of part image. In this case,low-resolution shape data output from second down sampling portion 1002are used as information on the boundary of the part image.

[0038] An upper layer coding portion 1003 codes pixel data of highresolution, in which the international standard method of motion imagecoding such as MPEG or H.261 is also employed. Here, prediction from thedecoded images in the lower layer as well as in the upper layer isemployed. For the boundary of the part image, high-resolution shape datathat have not been down sampled are used.

[0039] A shape data coding portion 1005 codes shape data of highresolution that corresponds to the resolution of the upper layer. Thecontour of a shape is expressed with 8 directional chain codes, forexample, and these chain codes are coded by Huffman coding.

[0040] The coded data are integrated by an integration portion (notshown), and transmitted or stored. In a decoding apparatus for decodingonly a lower layer, as shown in FIG. 11, only the data necessary fordecoding the lower layer are picked up from the coded data having thosefor the upper and lower layers integrated therein, and are used for thedecoding process. In other words, “coded data of the lower layer pixeldata” and “coded data of the shape data” are selected at a selectionportion (not shown) and decoded.

[0041] At this time, a shape data decoding portion 1103 in FIG. 11decodes high-resolution shape data. Low-resolution shape data areobtained in a down sampling portion 1102, using the same technique as insecond down sampling portion 1002 of FIG. 10. Thus obtained data areused for decoding pixel data in a lower layer decoding portion 1101. Adecoding apparatus for decoding up to an upper layer uses all the codeddata to conduct decoding up to the upper layer.

[0042] However, the above-described apparatus suffers the followingproblem. That is, though conventional decoding of a lower layer onlyrequires shape data of low resolution, the above apparatus has to usehigh-resolution shape data when coding data in the lower layer, whichresults in redundant data. In other words, shape data in an upper layerhaving a large amount of codes should be used instead of shape data in alower layer with a less amount of codes. Therefore, it becomes difficultto code a lower layer in good image quality with a limited transmissionor storage capacity.

[0043] The first and second embodiments of the present invention aim tosolve this problem.

[0044]FIGS. 1 and 2 are block diagrams respectively showing a codingapparatus and a decoding apparatus according to the first embodiment.

[0045] Referring to FIG. 1, a down sampling portion 104 thins out inputpixel data to generate low-resolution pixel data for a lower layer. Whenthinning out, a low path filter is used to prevent aliasing. A lowerlayer coding portion 105 codes the low-resolution pixel data.

[0046] For coding, the internationally standardized method of codingmotion images, such as MPEG or H.261, is employed. When an image isdivided into blocks, an arbitrary shape DCT technique or the like isemployed for a block including a boundary of part image. For theboundary of the part image, low-resolution shape data output from afirst shape data generating portion 106 are used.

[0047] First shape data generating portion 106 generates low-resolutionshape data for a lower layer. Shape data are extracted by dividing pixeldata into areas, for example. Techniques used for the area dividinginclude an edge detecting technique using differential operation, andmorphological segmentation.

[0048] When cutting out a shape of moving object from a staticbackground, dynamic area detection using intra-frame differences can beutilized. Alternatively, shape data can be generated by chromakeytechnique. In FIG. 1, low-resolution shape data are obtained afterthinning out target pixel data in a down sampling portion 104 to lowerthe resolution thereof. However, another method may be employed in whichshape data are first obtained for high-resolution pixel data, and theshape data are then thinned out to obtain low-resolution shape data.

[0049] The shape data generated here are binary images or images havingtwo or more levels of gradation. In the latter case, superimposition ofa part image and a background image according to the above expression(1) can be considered as weighted mean of the part image and thebackground image with the shape data being a weight. Note that the shapedata s (i,j) in the expression (1) takes a value “1” within the targetpart image, “0” outside the part image, and a value between “0” and “1”at the boundary portion of the part image.

[0050] A first shape data coding portion 107 codes low-resolution shapedata for a lower layer. If the shape data are binary data, run lengthcoding, MMR coding, chain coding, or the like is used for the coding. Ifthe shape data are expressed with two or more levels of gradation, acoding scheme using DCT as in MPEG, a coding scheme using a quaternarytree and vector quantization (“MPEG-4 Video Verification Model Version2.0” (ISO/IECTC1/SC29/WG11 N1260)), or the like is used.

[0051] A second shape data generating portion 102 generateshigh-resolution shape data for an upper layer from high-resolution pixeldata. The method of generating the shape data is same as in the firstshape data generating portion 106, and therefore, description thereof isnot repeated. A second shape data coding portion 103 codes thehigh-resolution shape data generated by second shape data generatingportion 102. The method of coding the shape data is same as in the firstshape data coding portion 107, and description thereof is not repeated.Note that those two shape data coding portions 103, 107 do not have touse the identical coding method; they may use separate methods forcoding, instead.

[0052] An upper layer coding portion 101 codes high-resolution pixeldata. The coding is performed using the international standard method ofcoding motion images, such as MPEG or H.261, as in the techniquedescribed in the Background Art section. Herein, however, the codingutilizes prediction from partially decoded images existing in lowerlayer coding portion 105 in addition to prediction from decoded imagespreceding or succeeding in time in the upper layer. For the boundary ofpart image, high-resolution shape data output from second shape datagenerating portion 102 are used.

[0053] Next, a decoding apparatus according to the first embodiment willbe described with reference to FIG. 2.

[0054] A lower layer decoding apparatus 205 consists of portionssurrounded by a broken line in FIG. 2. A first shape data decodingportion 204 decodes coded data of the lower layer shape data to obtainlow-resolution shape data. The decoded shape data are sent to a lowerlayer decoding portion 203, and are also used for display of a lowerlayer image. Lower layer decoding portion 203 decodes coded data of thelower layer pixel data, and supplies low-resolution pixel data to alower layer display portion (not shown).

[0055] Next, decoding of an upper layer in FIG. 2 will be described. Asecond shape data decoding portion 202 decodes coded data of the upperlayer shape data to obtain high-resolution shape data. The decoded shapedata are sent to an upper layer decoding portion 201, and also used fordisplay of an upper layer image.

[0056] Upper layer decoding portion 201 decodes coded data of the upperlayer pixel data, and supplies high-resolution pixel data to an upperlayer display portion (not shown). Upper layer decoding portion 201utilizes, as in the upper layer coding portion 101 shown in FIG. 1,prediction from the decoded images in lower layer decoding portion 203in addition to prediction from the decoded images preceding orsucceeding in time in the upper layer.

[0057] The second embodiment of the present invention will now bedescribed.

[0058] In the first embodiment described above, high-resolution shapedata used in an upper layer and low-resolution shape data used in alower layer are coded independent of each other. Thus, information onthe shape data in the lower layer is not reflected to coding of theshape data in the upper layer, and therefore, an amount of codes of theshape data in the upper layer becomes large. This leads to a problemthat a total amount of codes for the upper layer increases than in thecase where the methods shown in FIGS. 10 and 11 are employed.Accordingly, this embodiment aims to solve the above problem by codingonly information on the difference between low-resolution shape data andhigh-resolution shape data.

[0059]FIGS. 3 and 4 are block diagrams respectively showing a codingapparatus and a decoding apparatus according to the second embodiment.

[0060] The coding apparatus in FIG. 3 differs from the coding apparatusin FIG. 1 in that low-resolution shape data in a first shape data codingportion 307 are sent to a second shape data coding portion 303, and thesecond shape data coding portion 303 codes only information on thedifference between the low-resolution shape data and the high-resolutionshape data.

[0061] Other than that, upper layer coding portion 101, second shapedata generating portion 102, down sampling portion 104, lower layercoding portion 105, and first shape data generating portion 106 are thesame as those in FIG. 1, and therefore, description thereof is notrepeated.

[0062] The decoding apparatus in FIG. 4 is different from the decodingapparatus in FIG. 2 in that low-resolution shape data decoded in a firstshape data decoding portion 404 are sent to a second shape data decodingportion 402, and the second shape data decoding portion 402 decodeshigh-resolution shape data along with the information on the difference.

[0063] Other than that, upper layer decoding portion 201 and lower layerdecoding portion 203 are same as those in FIG. 2, and therefore,description thereof is not repeated. In addition, a lower layer decodingapparatus 405 is equivalent to lower layer decoding apparatus 205 inFIG. 2.

[0064] When a quaternary tree is used for representing binary shapedata, for example, data in the lower hierarchies of the tree may be usedas the above-described information on the difference. FIG. 7 showsbinary shape data and exemplary quaternary tree representation thereof.The uppermost value of the quaternary tree is “1” when at least onepixel value “1” exists within a block of 4 pixels by 4 pixels, or “0”otherwise. Values at the second and the third hierarchies of the treeare likewise determined for blocks of 2 pixels by 2 pixels and of 1pixel by 1 pixel, respectively.

[0065] Blocks at respective hierarchies are scanned from above left tobelow right in a raster scan sequence. In the example shown in FIG. 7,the shape data in the upper layer are expressed with three hierarchies,and the shape data in the lower layer are expressed with twohierarchies. The data in the third hierarchy is expressed as theinformation on the difference between the upper and lower layers. Thesedata expressed with the quaternary tree are coded by arithmetic coding,for example.

[0066] When the shape data are expressed with two or more layers ofgradation, another coding method may be employed, in whichlow-resolution shape data are up-sampled to the resolution for an upperlayer before taking the difference with high-resolution shape data, andthe difference data are then coded by transformation coding.

[0067] Next, the third embodiment of the present invention will bedescribed.

[0068] In the methods described with reference to FIGS. 10 and 11 asabove, low-resolution shape data are obtained by thinning out shapedata. This may cause a problem that the contour of a part image in thelower layer becomes stepwise, which results in degradation of the imagequality.

[0069] In the third embodiment, the above problem is solved by settingup for shape data more layers of gradation than in the original shapedata, along with thinning out of the shape data.

[0070]FIG. 8A shows a part of binary shape data. FIG. 8B shows exemplaryshape data transformed to be adapted to a low-resolution monitor ofwhich the resolution is halved and the pixel size is doubled bothvertically as well as horizontally. In this example, a 2×2 filter, 0.250.25 0.25 0.25,

[0071] is applied to a block surrounded by a bold line in FIG. 8A,thereby obtaining low-resolution shape data having five levels ofgradation of 0, 0.25, 0.5, 0.75, and 1. When an element of the above 2×2filter is represented as f (i, j) and an element within a block in FIG.8A is represented as d (i, j), the filtering operation can berepresented as follows:

[0072] Σf(i, j) d (i, j)

[0073] wherein Σ represents a sum for i=1, 2 and j=1, 2. If the originalshape data has N levels of gradation, the filtering allows generation ofshape data with M(M>N) levels of gradation.

[0074]FIG. 8C shows exemplary shape data used for enlarging a part imageof low resolution for display on a monitor that allows display with thesame resolution as in FIG. 8A. The data can be obtained by simplyenlarging the data in FIG. 8B by a factor of 2 vertically as well ashorizontally. Increasing the number of levels of gradation of the shapedata in low resolution as described above can avoid the stepwiseappearance of the boundary portion.

[0075] The shape data generated in FIG. 8C, for example, can be used forsuperimposing images according to the expression (1) described in theBackground Art section. In this case, the background and the foregroundare mixed at the contour portion of a part image, thereby making thestepwise pattern at the boundary inconspicuous.

[0076] Though the above example has been described using a 2×2 filter,other filters may be employed, instead. For example, a 3×3 filter asfollows can be used to transform shape data into a vertically as well ashorizontally halved version. 0 1/6 0 1/6 2/6 1/6 0 1/6 0

[0077] Here, target pixels for sub-sampling are, for example, thoseshown by in FIG. 8(d).

[0078]FIGS. 5 and 6 are block diagrams respectively showing a codingapparatus and a lower layer decoding apparatus according to the thirdembodiment. They are modifications of those that are shown in FIGS. 10and 11, with the portions for down sampling the shape data beingreplaced by transforming portions 504 and 602, respectively.

[0079] Other than that, first down sampling portion 1001, upper layercoding portion 1003, lower layer coding portion 1004, shape data codingportion 1005, lower layer decoding portion 1101, and shape data decodingportion 1103 are same as those in FIGS. 10 and 11, and therefore,description thereof is not repeated.

[0080] Transforming portions 504 and 602, each operating identical toeach other, transform shape data into the ones having lower resolutionbut more levels of gradation, as shown in FIG. 8.

[0081] Though a 2×2 filter has been used in FIGS. 8A-8C, many otherfilters, such as those of 3×3 or 2×5, can also be used fortransformation.

[0082] Furthermore, in the description of the coding apparatus accordingto the above embodiments, shape data sent to the shape data codingportion have also been sent to the corresponding pixel data codingportion. In that case, however, a problem will arise when nonreversiblecoding is performed in the shape data coding portion, because the shapedata used in a pixel data coding portion and the shape data used in apixel data decoding portion in a decoding apparatus become differentfrom each other.

[0083] In such a case, the coding apparatus may be provided with a shapedata decoding portion, so that the coded shape data can be decoded inthe shape data decoding portion before being sent to the correspondingpixel data coding portion. FIG. 9 shows a variation of the codingapparatus in FIG. 3, which has been modified in this manner.

[0084] Referring to FIG. 9, decoded data of the lower layer shape datathat have been decoded by a first shape data decoding portion 909 aresent to a lower layer coding portion 905 as well as to a second shapedata coding portion 903 and a second shape data decoding portion 908. Adecoding apparatus corresponding to the coding apparatus shown in FIG. 9also uses the decoded data of lower layer shape data at an upper layershape data decoding portion, that is a portion equivalent to the secondshape data decoding portion 908 in FIG. 9.

[0085] Finally, the fourth embodiment of the present invention will bedescribed.

[0086] The present embodiment is based on the first and secondembodiments, but in which an upper layer is configured to improvespatial resolution of only a portion of part image coded in the lowerlayer. By this configuration, an area for a face of a figure can becoded as a part image in the lower layer, and only the mouth portion canbe coded in high resolution in the upper layer, for example.

[0087] When the fourth embodiment is adapted to the first embodiment,the second shape data generating portion 102 of the coding apparatusshown in FIG. 1 can be used to generate high-resolution shape datacorresponding to a portion of part image, and thus the present inventioncan be implemented.

[0088] As a decoding apparatus corresponding thereto, the apparatusshown in FIG. 2 can be used as it is. Likewise, when this embodiment isadapted to the second embodiment, the high-resolution shape datacorresponding to a portion of part image can be generated by the secondshape data generating portion 102 of the coding apparatus shown in FIG.3, whereby the present invention can be implemented.

[0089] In this case, however, a signal line from the first shape datacoding portion 307 to the second shape data coding portion 303 is notused. Therefore, there is a need to provide a switch to switch betweenthe methods described in the fourth and second embodiments. This switchis provided between the first shape data coding portion 307 and thesecond shape data coding portion 303. When using the method according tothe fourth embodiment, the switch is turned off and the upper layershape data (the second shape data) are coded independently. When usingthe method as described in the second embodiment, the switch is turnedon and the information on the difference between the upper layer shapedata (the second shape data) and the lower layer shape data (the firstshape data) are coded.

[0090] For a decoding apparatus, the apparatus shown in FIG. 4 isprovided with a similar switch, which is disposed on a signal lineconnecting the first shape data decoding portion 404 and the secondshape data decoding portion 402 in FIG. 4. The switch, as with theswitch in the coding apparatus, controls switching between the case inwhich the upper layer shape data (the second shape data) are decodedindependently, and the case in which the data representing thedifference between the upper layer shape data (the second shape data)and the lower layer shape data (the first shape data) are decoded andthen the difference data are added to the lower layer shape data (thefirst shape data) to decode the upper layer shape data (the second shapedata).

[0091] According to the motion image coding apparatus and the motionimage decoding apparatus according to the above embodiments, thefollowing favorable effects can be obtained:

[0092] (1) Coding and decoding of a part image having spatial hierarchycan be realized.

[0093] (2) In the first embodiment, low-resolution shape data are codedas the shape data for a lower layer. Accordingly, redundancy associatedwith coding of high-resolution shape data in the lower layer can beeliminated. Therefore, an image in the lower layer can be coded anddecoded in desirable image quality, even with limited transmission orstorage capacity.

[0094] (3) In the second embodiment, information on the shape data inthe lower layer is used for coding the shape data in the upper layer,and information on the difference between the low-resolution shape dataand the high-resolution shape data is coded. Accordingly, data amountnecessary for coding the shape data in the upper layer can be reduced.Therefore, efficient coding can be realized in the upper layer.

[0095] (4) In the third embodiment, upper layer shape data aretransformed to generate lower layer shape data having more levels ofgradation. Accordingly, the stepwise boundary existing in the contourportion of lower layer shape data can be made inconspicuous. Therefore,the contour of a part image on display becomes smooth, and thus apsychically favorable image can be obtained.

[0096] (5) In another embodiment of the present invention, assuming thatthe upper layer shape data are smaller than the lower layer shape data,hierarchical coding for improving spatial resolution of a part of thelower layer using data in the upper layer can be performed. Accordingly,if there is a need to look into the contents of an image only in aportion of the lower layer, or if only a portion in the lower layer hasa complex texture and has to be displayed in high resolution, it ispossible to perform an appropriate hierarchical coding.

INDUSTRIAL APPLICABILITY

[0097] As described above, the present invention enables efficientcoding and decoding of a part image having spatial hierarchy.Accordingly, the present invention is advantageously applicable to thefield of image coding and decoding apparatuses.

1. An image coding apparatus performing lower layer coding for coding apart image in arbitrary shape in low resolution and upper layer codingfor coding the part image in high resolution, comprising: a first shapedata generating portion (106) for generating low-resolution shape datarepresenting the arbitrary shape; a first shape data coding portion(107) for coding the generated low-resolution shape data; a second shapedata generating portion (102) for generating high-resolution shape datarepresenting the arbitrary shape; and a second shape data coding portion(103) for coding the generated high-resolution shape data; wherein saidlow-resolution shape data are used for coding the part image in thelower layer, and said high-resolution shape data and said decoded partimage data in the lower layer are used for coding the part image in theupper layer.
 2. The image coding apparatus according to claim 1, whereinsaid second shape data coding portion codes information on differencebetween said high-resolution shape data and said low-resolution shapedata.
 3. An image coding apparatus performing lower layer coding forcoding a part image in arbitrary shape in low resolution and upper layercoding for coding the part image in high resolution, whereinhigh-resolution shape data of said part image are shared by the upperand lower layers; the image coding apparatus comprising: ahigh-resolution shape data generating portion for generatinghigh-resolution shape data of said part image; and a shape data codingportion (105) for coding the generated high-resolution shape data;wherein said high-resolution shape data having N levels of gradation (Nis at least 2) are transformed to low-resolution shape data having M(M>N) levels of gradation, said low-resolution shape data are used forcoding the part image in the lower layer, and said high-resolution shapedata and decoded part image data in the lower layer are used for codingthe part image in the upper layer.
 4. An image decoding apparatus fordecoding data coded by the image coding apparatus according to claim 1,performing lower layer decoding for decoding a part image in arbitraryshape in low resolution and upper layer decoding for decoding the partimage in high resolution; the image decoding apparatus comprising: afirst shape data decoding portion (204) for decoding low-resolutionshape data; and a second shape data decoding portion (202) for decodinghigh-resolution shape data; wherein said low-resolution shape data areused for decoding the part image in the lower layer, and saidhigh-resolution shape data and decoded part image data in the lowerlayer are used for decoding the part image in the upper layer.
 5. Animage decoding apparatus for decoding data coded by the image codingapparatus according to claim 2, performing lower layer decoding fordecoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution; the imagedecoding apparatus comprising: a first shape data decoding portion (404)for decoding low-resolution shape data; and a second shape data decodingportion (402) for decoding high-resolution shape data; wherein saidlow-resolution shape data are used for decoding the part image in thelower layer, and said high-resolution shape data and said decoded partimage data in the lower layer are used for decoding the part image inthe upper layer, and said second shape data decoding portion (402) usesinformation on difference between said high-resolution shape data andsaid low-resolution shape data to obtain shape data in high resolution.6. An image decoding apparatus for decoding data coded by the imagecoding apparatus according to claim 3, performing lower layer decodingfor decoding a part image in arbitrary shape in low resolution and upperlayer decoding for decoding the part image in high resolution, whereinhigh-resolution shape data of said part image are shared in the lowerand upper layers; the image decoding apparatus comprising: a shape datadecoding portion (1103) for decoding high-resolution shape data; whereinsaid high-resolution shape data having N (N is at least 2) levels ofgradation are transformed to low-resolution shape data having M (M>N)levels of gradation, said transformed shape data are used for decodingthe part image in the lower layer, and said high-resolution shape dataand said decoded part image in the lower layer are used for decoding thepart image in the upper layer.
 7. The image coding apparatus accordingto claim 1, wherein said second shape data generating portion (102) hasa mode for generating high-resolution shape data corresponding to aportion of the part image coded in the lower layer.
 8. The image codingapparatus according to claim 2, wherein said second shape datagenerating portion (102) has a mode for generating high-resolution shapedata corresponding to a portion of the part image coded in the lowerlayer, and when said mode is selected, said second shape data codingportion codes said high-resolution shape data independent of saidlow-resolution shape data.
 9. An image decoding apparatus for decodingdata coded by the image coding apparatus according to claim 7,performing lower layer decoding for decoding a part image in arbitraryshape in low resolution and upper layer decoding for decoding the partimage in high resolution; the image decoding apparatus comprising: afirst shape data decoding portion for decoding low-resolution shapedata; and a second shape data decoding portion for decodinghigh-resolution shape data; wherein said low-resolution shape data areused for decoding the part image in the lower layer, and saidhigh-resolution shape data and said decoded part image data in the lowerlayer are used for decoding the part image in the upper layer, and saidsecond shape data decoding portion has a mode for decodinghigh-resolution shape data corresponding to a portion of the part imagecoded in the lower layer.
 10. An image decoding apparatus for decodingdata coded by the image coding apparatus according to claim 8,performing lower layer decoding for decoding a part image in arbitraryshape in low resolution and upper layer decoding for decoding the partimage in high resolution; the image decoding apparatus comprising: afirst shape data decoding portion for decoding low-resolution shapedata; and a second shape data decoding portion for decodinghigh-resolution shape data; wherein low-resolution shape data are usedfor decoding the part image in the lower layer, and said high-resolutionshape data and said decoded part image data in the lower layer are usedfor decoding the part image in the upper layer, said second shape datadecoding portion obtains high-resolution shape data by using informationon difference between said high-resolution shape data and saidlow-resolution shape data, and said second shape data decoding portionhas a mode for decoding high-resolution shape data corresponding to aportion of the part image coded in the lower layer, and, when said modeis selected, decodes said high-resolution shape data independent of saidlow-resolution shape data